by A program in execution is called a process. There can be multiple instances of a program running in the system which are identified by a unique id called process id. Operating System ensures that each process has a unique id which is always a non-negative integer number.
A thread is a lightweight process which can only be used inside a process. Like process, thread also has a unique identifier to identify threads which are called thread ids. Unlike process ids, thread ids are only unique to a process and one process threads are unknown to other process.
Process Vs Threads
| Process | Thread |
|---|---|
| A program in execution is called process. | Thread is a lightweight process which executes smaller portion of a process. |
| Process takes more time to create and terminate. | Thread takes lesser time to create and terminate. |
| Each process has its own time slot to run scheduled by the Operating system. Hence context switching is slower. | All threads share the same time slot of its parent process. Hence context switching is faster. |
| Process has its own control block, stacks, heaps. | Thread has its own control block and stack but shares parent process heaps etc. |
| Inter process communication required to interact between processes. | Since thread shares the same address space of parent processes, hence no extra method is required to share information. |
| Process can be created using fork () method. | Thread can be created using pthread_create () method. |
